Conventionally, a proximity sensor described in Japanese Patent Publication No. 2010-45531 (JP2010-45531A) is provided as a device for detecting an object in a non-contact manner. In a prior art described in JP2010-45531A, an oscillation circuit includes an LC resonance circuit having a detection coil and a capacitor. When the oscillation circuit is oscillated and an object including a metallic body (conductor) or a magnetic body approaches the detection coil, the conductance of the detection coil is decreased, and thus, oscillation of the oscillation circuit stops. Thus, the existence (approach) of the object is detected as the oscillation stops. In addition, in the prior art of JP2010-45531A, whether or not the disconnection of the detection coil occurs is detected by observing amplitude of oscillation (resonant voltage of the LC resonance circuit) of the oscillation circuit.
However, in the prior art of JP2010-45531A, since the oscillation of the oscillation circuit stops when the object approaches the detection coil, it is difficult to determine whether the oscillation is stopped by an abnormality (disconnection or short circuit of the detection coil) of the LC resonance circuit or the oscillation is stopped normally due to the approach of the object.